<div id="a1">
  <div class="container">
    <div class="row">
      <div class="jumbotron">
        <h1>Hello, world!</h1>
        <p>...</p>
        <p><a class="btn btn-primary btn-lg" href="#" role="button">Learn more</a></p>
      </div>
    </div>

  </div>
</div>
<div id="a2">
  <div class="container">
    <div class="row">
      <div class="panel panel-default">
        <div class="panel-heading">Panel heading without title</div>
        <div class="panel-body">
          Panel content
        </div>
      </div>

      <div class="panel panel-default">
        <div class="panel-heading">
          <h3 class="panel-title">Panel title</h3>
        </div>
        <div class="panel-body">
          Panel content
        </div>
      </div>
    </div>

  </div>
</div>
